Electrochemical compressor and refrigeration system

ABSTRACT

A refrigeration system defines a dosed loop that contains a working fluid, at least part or the working fluid being circulated through the dosed loop. The refrigeration system includes a first heat transfer device that transfers heat from the first heat reservoir to the working fluid, a second heat transfer device that transfers heat from the working fluid to the second heat reservoir, and an electrochemical compressor between the first and second heat transfer devices. The electrochemical compressor includes one or more electrochemical Cells electrically connected to each other through a power supply, each electrochemical cell including a gas pervious anode, a gas pervious cathode, and an electrolytic membrane disposed between and in intimate electrical contact with the cathode and the anode. The working, fluid includes a condensable refrigerant that bypasses the electrochemical process; and an electrochemically active fluid that participates in die electrochemical process within the electrochemical compressor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/626,416, filed on Nov. 25, 2009 and entitled ElectrochemicalCompressor and Refrigeration System, currently pending, which claimspriority to U.S. Application No. 61/200,714, filed on Dec. 2, 2008 andentitled “Electrochemical Compressor and Heat Pump System,”; both ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The disclosed subject matter relates to a refrigeration system thatincludes a vapor-compression refrigeration cycle that includes anelectrochemical compressor configured to transfer a refrigerant.

BACKGROUND

The function of both refrigeration cycles and heat pumps is to removeheat from a heat source or reservoir at low temperature and to rejectthe heat to a heat sink or reservoir at high temperature. While manythermodynamic effects have been exploited in the development of heatpumps and refrigeration cycles, the most popular today is the vaporcompression approach. This approach is sometimes called mechanicalrefrigeration because a mechanical compressor is used in the cycle.

Mechanical compressors account for approximately 30% of a household'senergy requirements and thus consume a substantial portion of mostutilities' base load power. Any improvement in efficiency related tocompressor performance can have significant benefits in terms of energysavings and thus have significant positive environmental impact. Inaddition, there are increasing thermal management problems in electroniccircuits, which require smaller heat pumping devices with greaterthermal management capabilities.

Vapor compression refrigeration cycles generally contain five importantcomponents. The first is a mechanical compressor that is used topressurize a gaseous working fluid. After proceeding through thecompressor, the hot pressurized working fluid is condensed in acondenser. The latent heat of vaporization of the working fluid is givenup to a high temperature reservoir often called the sink. The liquefiedworking fluid is then expanded at substantially constant enthalpy in athermal expansion valve or orifice. The cooled liquid working fluid isthen passed through an evaporator. In the evaporator, the working fluidabsorbs its latent heat of vaporization from a low temperature reservoiroften called a source. The last element in the vapor compressionrefrigeration cycle is the working fluid itself.

In conventional vapor compression cycles, the working fluid selection isbased on the properties of the fluid and the temperatures of the heatsource and sink. The factors in the selection include the specific heatof the working fluid, its latent heat of vaporization, its specificvolume and its safety. The selection of the working fluid affects thecoefficient of performance of the cycle.

For a refrigeration cycle operating between a lower limit, or sourcetemperature, and an upper limit, or sink temperature, the maximumefficiency of the cycle is limited to the Carnot efficiency. Theefficiency of a refrigeration cycle is generally defined by itscoefficient of performance, which is the quotient of the heat absorbedfrom the sink divided by the net work input required by the cycle.

SUMMARY

In one general aspect, a refrigeration system conveys heat from a firstheat reservoir at a relatively low temperature to a second heatreservoir at relatively high temperature. The refrigeration systemdefines a closed loop that contains a working fluid, at least part ofthe working fluid being circulated through the closed loop. Therefrigeration system includes a first heat transfer device thattransfers heat from the first heat reservoir to the working fluid, asecond heat transfer device that transfers heat from the working fluidto the second heat reservoir, an expansion valve between the first andsecond heat transfer devices that reduces pressure of the working fluid,and an electrochemical compressor between the first and second heattransfer devices. The electrochemical compressor includes one or moreelectrochemical cells electrically connected to each other through apower supply, each electrochemical cell including a gas pervious anode,a gas pervious cathode, and an electrolytic membrane disposed betweenand in intimate electrical contact with the cathode and the anode.

Implementations can include one or more of the following features. Forexample, the working fluid can include a condensable refrigerant thatbypasses the electrochemical process; and an electrochemically activefluid that participates in the electrochemical process within theelectrochemical compressor.

In other implementations, the working fluid can include a condensablerefrigerant; water; and an electrochemically active fluid. In otherimplementations, the working fluid includes a condensable refrigerantthat is not water; and an electrochemically active fluid. In someimplementations, the condensable refrigerant does not participate in theelectrochemical process.

The working fluid can include carbon dioxide. The working fluid caninclude a fluorocarbon gas. The electrolytic membrane can include asolid electrolyte, for example, a gel.

The refrigeration system can include a temperature sensor thermallycoupled to one or more of the working fluid, the first heat transferdevice, and the second heat transfer device. The first heat transferdevice can include a condenser. The second heat transfer device caninclude an evaporator.

The electrochemical compressor can include a cathode gas space on anonelectrolyte side of the cathode; and an anode gas space on anonelectrolyte side of the anode. The electrochemical compressor caninclude a first electrochemically active route that traverses the anodeand cathode; a second non-electrochemical route that bypasses the anodeand cathode; and a combiner that combines the components that havetraversed the first and second routes.

The refrigeration system can also include a mechanical compressor. Themechanical compressor can be in series with the electrochemicalcompressor. The mechanical compressor can be between the electrochemicalcompressor and the first heat transfer device. The mechanical compressorcan be between the electrochemical compressor and second heat transferdevice.

In another general aspect, an electrochemical compressor includes aninlet fluidly coupled to an evaporator to receive a working fluid thatcomprises a condensable refrigerant and an electrochemically activefluid; an outlet fluidly coupled to a condenser; and one or moreelectrochemical cells electrically connected to each other through apower supply. Each electrochemical cell includes a gas pervious anode, agas pervious cathode, and an electrolytic membrane disposed between andin intimate electrical contact with the cathode and the anode. Theanode, the cathode, and the electrolytic membrane are configured to passthe electrochemically active fluid. The electrochemical cell isconfigured to disassociate the condensable refrigerant from theelectrochemically active fluid to prevent the condensable refrigerantfrom passing through the anode, the cathode, and the electrolyticmembrane. The electrolytic membrane includes a membrane having a porousmicrostructure and an ion exchange material impregnated throughout themembrane.

Implementations can include one or more of the following features. Forexample, the impregnated membrane can have a Gurley number of greaterthan 10,000 seconds.

The ion exchange membrane can be able to withstand a pressure gradientbetween a side adjacent the anode and a side adjacent the cathode. Theion exchange membrane can be able to withstand a pressure gradient of atleast 30 psi between a side adjacent the anode and a side adjacent thecathode.

The ion exchange membrane can include a synthetic fluoropolymer oftetrafluoroethylene. The synthetic fluoropolymer can be an expandedpolytetrafiuoroethylene having a porous microstructure of polymericfibrils. The ion exchange material can substantially impregnate themembrane so as to render an interior volume of the membranesubstantially occlusive. The ion exchange material can be impermeable togas. The ion exchange material can be permeable to gas. The ion exchangematerial can be selected from a group consisting of perfluorinatedsulfonic acid resin, perfluorinated carboxylic acid resin, polyvinylalcohol, divinyl benzene, styrene-based polymers, and metal salts withor without a polymer.

The anode, the cathode, and the electrolytic membrane can be configuredto pass the electrochemically active fluid if the working fluid includesless than 50% of water.

The one or more electrochemical cells can be connected in parallel witheach other.

A first electrochemically active route can be defined by the anode, theelectrolytic membrane, and the cathode; and a second non-electrochemicalroute bypasses the anode, the electrolytic membrane, and the cathode.

The compressor can include a combiner that combines the components ofthe working fluid that have traversed the first, route, the secondroute, or both the first and second routes.

The ion exchange material can include a liquid electrolyte embedded in amatrix. The ion exchange material can include an anionic exchangemembrane and the anode gas space operates at a higher pressure than thecathode gas space.

The porous membrane can have a total thickness of less than 0.025 mm.

In another general aspect, a method of refrigeration includes conveyingheat from a first heat reservoir at a relatively low temperature to asecond heat reservoir at relatively high temperature by circulating aworking fluid through a closed loop that is thermally coupled to thefirst heat reservoir at a first portion and is thermally coupled to thesecond heat reservoir at a second portion. The conveying includestransferring heat from the working fluid at the second loop portion tothe second heat reservoir including liquefying at least some of theworking fluid; reducing a pressure of the at least partially liquefiedworking fluid by expanding the working fluid at a substantially constantenthalpy; and transferring heat from the first heat reservoir to theworking fluid at the first loop portion including vaporizing at leastsome of the working fluid. The conveying also includes increasing apressure of the working fluid by dissociating an electrochemicallyactive fluid from a condensable refrigerant within the working fluid toenable the condensable refrigerant to separate from theelectrochemically active fluid, electrochemically ionizing theelectrochemically active fluid by stripping charged particles from theelectrochemically active fluid, enabling the ionized electrochemicallyactive fluid to pass through an electrolytic membrane, pumping thecharged particles to create an electric potential gradient across theelectrolytic membrane, pumping the ionized electrochemically activefluid across the electrolytic membrane using the electric potentialgradient, electrochemically de-ionizing the electrochemically activefluid by combining the pumped charged particles with the ionizedelectrochemically active fluid, and pressuring the de-ionizedelectrochemically active fluid. The conveying further includesre-associating the pressurized de-ionized electrochemically active fluidwith the condensable refrigerant to form a pressurized working fluidthat flows to the second loop portion.

Implementations can include one or more of the following features. Forexample, dissociating the electrochemically active fluid from thecondensable refrigerant can include passing the working fluid through ananode gas space to thereby dissociate the electrochemically active fluidfrom the condensable refrigerant within the working fluid.Electrochemically ionizing the electrochemically active fluid bystripping charged particles from the electrochemically active fluid caninclude electrochemically ionizing the electrochemically active fluidwithin a gas pervious anode adjacent the anode gas space. Enabling theionized electrochemically active fluid to pass through the electrolyticmembrane can include enabling the ionized electrochemically active fluidto enter the electrolytic membrane that is disposed between the gaspervious anode and a gas pervious cathode.

Pumping the charged particles to create the electric potential gradientacross the electrolytic membrane can include pumping electrons from thegas pervious anode to the gas pervious cathode to create the electricpotential gradient between the gas pervious anode and the gas perviouscathode, and pumping the ionized electrochemically active fluid acrossthe electrolytic membrane using the electric potential gradient caninclude pumping the ionized electrochemically active fluid to the gaspervious cathode.

Electrochemically de-ionizing the electrochemically active fluid caninclude combining the pumped charged particles in the gas perviouscathode with the ionized electrochemically active fluid, and pressuringthe de-ionized electrochemically active fluid can include pressuring thede-ionized electrochemically active fluid within a cathode gas spacethat is adjacent the gas pervious cathode and is maintained at a higherpressure than the anode gas space.

The method can also include controlling the amount of heat conveyed byvarying one or more of a current and a voltage applied to pump thecharged particles to create the electric potential gradient across theelectrolytic membrane.

There are several benefits to using carbon dioxide as a refrigerant in arefrigeration system. If carbon dioxide manages to leak out of thesystem, and make its way up to the ozone layer, the ultravioletradiation does not break up the molecule to release highly activechlorine radicals that help to deplete the ozone layer. Therefore,carbon dioxide does not deplete the ozone layer.

Moreover, while many have noted a few problems associated with the useof carbon dioxide in refrigeration systems, for example, requiringoperating at higher pressure and higher compressor temperature, theseoperating requirements are found to be more advantageous in automotiveapplications. The very high cycle pressure results in a high fluiddensity throughout the cycle, allowing miniaturization of the systemsfor the same heat pumping power requirements. Furthermore, the highoutlet temperature of the compressor can permit faster defrosting ofautomobile windshields and can even be used for combined space heatingand hot water heating in home usage. In fuel cell applications involvingthe production of hydrogen from hydrocarbon sources such as natural gas,hydrogen gas is fed to the electrode assembly as a mixed gas stream withcarbon dioxide present (typically referred to as reformate). Thus,electrodes have been developed and are commercially available (such asW. L. Gore & Associates Inc. series 56 PRIMEA assembly) with suitableelectrochemical performance with mixed hydrogen and carbon dioxide gasstreams.

The vapor compression refrigeration system uses an electrochemicalcompressor and therefore is modular (that is, it can be of differentsizes without limitation). The vapor compression refrigeration system iselectrically driven and thus fully electronically controlled. The vaporcompression refrigeration system can be considered essentiallynoiseless, and thus is less noisy than conventional mechanicalrefrigeration systems. The vapor compression refrigeration system ismore efficient than conventional mechanical refrigeration systems.

DRAWING DESCRIPTION

FIG. 1 is block diagram of an exemplary refrigeration system thatdefines a closed loop that contains a working fluid and includes anelectrochemical compressor.

FIG. 2 is block diagram of an electrochemical compressor and componentsof a working fluid that can be used in the refrigeration system of FIG.1.

FIGS. 3A-3C are block diagrams of electrochemical compressors thatinclude a plurality of electrochemical cells and can be used in therefrigeration system of FIG. 1.

FIG. 4A is a flow chart of a procedure performed by the refrigerationsystem of FIG. 1.

FIG. 4B is a flow chart of a procedure performed by a control systemwithin the refrigeration system of FIG. 1.

FIG. 5 is a block diagram of an exemplary refrigeration system thatdefines a closed loop that contains a working fluid and includes anelectrochemical compressor and a mechanical compressor in parallel witheach other.

FIG. 6 is a block diagram of an exemplary refrigeration system thatdefines a closed loop that contains a working fluid and includes anelectrochemical compressor and a mechanical compressor in series witheach other.

DESCRIPTION

Referring to FIG. 1, an exemplary refrigeration system 100 defines aclosed loop that contains a working fluid. The system 100 includes anelectrochemical compressor 105 that lacks moving parts, a first heattransfer device 110 that transfers heat from a first heat reservoir (aheat source or object to be cooled) to the working fluid, a second heattransfer device 115 that transfers heat from the working fluid to asecond heat reservoir (a heat sink), and a thermostatic expansion valve120 between the first and second heat transfer devices. The system 100also includes one or more sensors (for example, temperature sensors)125, 130 placed along flow paths between components of the system 100 toprovide feedback to a control system 135 that is also coupled to thecompressor 105, the first heat transfer device 110, and the second heattransfer device 115.

The working fluid contained within the closed loop of the system 100includes at least a first component that is electrochemically active andtherefore takes part in the electrochemical process within thecompressor 105. The working fluid includes at least a second componentthat is a condensable refrigerant that can be used for the heat pumpapplication under consideration. The condensable refrigerant is anysuitable condensable composition that does not include water. Asdiscussed below, the condensable refrigerant bypasses theelectrochemical process within the compressor 105.

Additionally, the working fluid includes a third component that is waterto hydrate an ion exchange membrane within the compressor 105 (asdiscussed below). Water can be considered a contaminant of some standardrefrigerants, and it can negatively impact heat exchange performance ofthe refrigerant. Thus water as the third component of the working fluidcan be reduced for example, to a minimal amount that is needed toprovide enough hydration to one or more components of the compressor105.

In some implementations, the first component (which is electrochemicallyactive) includes hydrogen (H₂) and the second component (which is acondensable refrigerant) includes carbon dioxide (CO₂). In thisimplementation, the components are present in the proportion ofapproximately one part hydrogen and four parts of carbon dioxide byvolume. The relative proportions of hydrogen and carbon dioxide aregoverned by the desired relative efficiency of the electrochemicalcompressor 105 and the system 100. The quantity of water maintained inthe working fluid is governed by the thickness of membranes employed inthe compressor 105, the equivalent weight (acidity) of the ion exchangemedia employed in the compressor 105, and the amount of hydrogen in thesystem 100. Thinner membranes of higher equivalent weight (that is,lower acidity) employed in systems with lower proton capability requireless water. In general, the working fluid includes less than 50% ofwater, but can include less than 20%, less than 10%, or less than 1%water, depending on the application.

It should be noted that while hydrogen is being used primarily as theelectrochemically active component of the working fluid, hydrogen alsopossesses useful heat transfer properties. Hydrogen's low density, highspecific heat, and thermal conductivity make it a superior coolant.Hydrogen gas can be used as the heat transfer medium industrially in,for example, turbine generators. The presence of hydrogen gas within theworking fluid thus enhances the performance of the condensablerefrigerant; and provides thermal exchange opportunities at points awayfrom thermally conductive surfaces of the fluid conduits and the heattransfer devices.

The first heat transfer device 110 includes an evaporator that acts as aheat exchanger that places the working fluid in a heat exchangerelationship with the first heat reservoir or source of heat (forexample, a source fluid). The first heat transfer device 110 includesinlet and outlet ports coupled to respective conduits 111, 112 thatcontain the working fluid of the system 100. The second heat transferdevice 115 includes a condenser that acts as a heat exchanger thatplaces the working fluid in a heat exchange relationship with the secondheat reservoir or heat sink (for example, a sink fluid). The second heattransfer device 115 includes inlet and outlet ports coupled torespective conduits 116, 117 that contain the working fluid of thesystem 100.

The expansion valve 120 is an orifice that is able controls the amountof working fluid flow. The valve 120 can include a temperature sensingbulb filled with a similar gas as in the working fluid that causes thevalve to open against the spring pressure in the valve body as thetemperature on the bulb increases. As temperatures in the evaporator 110decrease, so does the pressure in the bulb and therefore on the springcausing the valve to close.

Referring also to FIG. 2, the electrochemical compressor 105 is a devicethat raises the pressure of a component of the working fluid 200 by anelectrochemical process. Accordingly, at least one component of theworking fluid must be electrochemically active. In particular, theelectrochemically active component (the first component) must beionizable. For example, the electrochemically active component isoxidizable at a gas pervious anode 205 of the compressor 105 and isreducible at a gas pervious cathode 210 of the compressor 105.

The design in which the compressor 105 includes only one exemplary cell202 is shown in FIG. 2. However, the electrochemical compressor 105 caninclude a plurality of electrochemical cells 302, as shown in FIGS.3A-C. In some implementations, the electrochemical compressor 105 is anannular stack of electrochemical cells electrically connected in seriessuch as, for example, the cells generally described in U.S. Pat. No.2,913,511 (Grubb); in U.S. Pat. No. 3,432,355 (Neidrach); and in U.S.Pat. No. 3,489,670.

Each cell 202 includes the anode 205, where the electrochemically activecomponent (EC) of the working fluid is oxidized; the cathode 210, wherethe electrochemically active component EC of the working fluid isreduced; and an electrolyte 215 that serves to conduct the ionic species(EC⁺) from the anode 205 to the cathode 210. The electrolyte 215 can bean impermeable solid ion exchange membrane having a porousmicrostructure and an ion exchange material impregnated through themembrane such that the electrolyte 215 can withstand an appreciablepressure gradient between its anode and cathode sides. The examplesprovided here employ impermeable ion exchange membranes, and theelectrochemically active component of the working fluid is remixed withthe working fluid after compression and thus the pressure of the workingfluid 200 is elevated prior to the condensation phase of therefrigeration process. However, a permeable ion exchange membrane isalso feasible with the working fluid traversing in a unidirectional andsequential path through electrode assemblies with increasing pressure.The active components of the working fluid dissolve into the ionexchange media of the ion exchange membrane and the gas in the workingfluid traverses through the ion exchange membrane.

As another example, the electrolyte 215 can be made of a solidelectrolyte, for example, a gel, that is, any solid, jelly-like materialthat can have properties ranging from soft and weak to hard and toughand being defined as a substantially dilute crosslinked system thatexhibits no flow when in the steady-state. The solid electrolyte can bemade very thin, for example, it can have a thickness of less than 0.2mm, to provide additional strength to the gel. Alternatively, the solidelectrolyte can have a thickness of less than 0.2 mm if it is reinforcedwith one or more reinforcing layers like a polytetrafluoroethylene(PTFE) membrane (having a thickness of about 0.04 mm or less) dependingon the application and the ion exchange media of the electrolyte.

Each of the anode 205 and the cathode 210 can be an electrocatalyst suchas platinum or palladium or any other suitable candidate catalyst. Theelectrolyte 215 can be a solid polymer electrolyte such as Nafion(trademark for an ion exchange membrane manufactured by the I. E. DuPontDeNemours Company) or GoreSelect (trademark for a composite ion exchangemembrane manufactured by W. L. Gore & Associates Inc.). The catalysts(that is, the anode 205 and the cathode 210) are intimately bonded toeach side of the electrolyte 215. The anode 205 includes an anode gasspace (a gas diffusion media) 207 and the cathode 210 includes a cathodegas space (a gas diffusion media) 212. The electrodes (the anode 205 andthe cathode 210) of the cell 202 can be considered as theelectrocatalytic structure that is bonded to the solid electrolyte 215.The combination of the electrolyte 215 (which can be an ion exchangemembrane) and the electrodes (the anode 205 and the cathode 210) isreferred to as a membrane electrode assembly or MEA.

Adjacent the anode gas space 207 is an anode current collector 209 andadjacent the cathode gas space 212 is a cathode current collector 214.The anode collector 209 and the cathode collector 214 are electricallydriven by the power supply 250. The anode collector 209 and the cathodecollector 214 are porous, electronically conductive structures that canbe woven metal screens (also available from Tech Etch) or woven carboncloth or pressed carbon fiber or variations thereof. The pores in thecurrent collectors 209, 214 serve to facilitate the flow of gases withinthe gas spaces 207, 212 adjacent to the respective electrodes 205, 210.

Outer surfaces of the collectors 209, 214 are connected to respectivebipolar plates 221, 226 that provide fluid barriers that retain thegases within the cell 202. Additionally, if the cell 202 is provided ina stack of cells, then the bipolar plates 221, 226 separate the anodeand cathode gases within each of the adjacent cells in the cell stackfrom each other and facilitate the conduction of electricity from onecell to the next cell in the cell stack of the compressor. The bipolarplate 221, 226 can be obtained from a number of suppliers including TechEtch (Massachusetts).

Additionally, subassemblies of components of the electrochemical cellcan be commercially obtained from manufacturers such as W. L. Gore &Associates Inc. under the PRIMEA trademark or Ion Power Inc.Commercially available assemblies are designed for oxygen reduction onone electrode and therefore the electrodes (the anode 205 and cathode210) may need to be modified for hydrogen reduction.

Hydrogen reduction at the cathode 210 actually requires lower loadingsof precious metal catalysts and also is feasible with alternative lowercost catalysts such as palladium. Thus, the eventual production costs ofassemblies employed in the system 100 are substantially lower thantypical fuel cell components.

As mentioned above, the control system 135 is coupled to the compressor105, the first heat transfer device 110, and the second heat transferdevice 115. The control system 135 is also coupled to one or moretemperature sensors 125, 130, 140, 145 placed within the system 100 tomonitor or measure the temperature of various features of the system100. For example, the temperature sensor 125 can be configured tomeasure the temperature of the working fluid within the conduit 111 andthe temperature sensor 130 can be configured to measure the temperatureof the working fluid within the conduit 117. As another example,temperature sensors 140, 145 can be placed near respective heat transferdevices 110, 115 to measure the temperature at which the heat transferdevice operates, to measure the temperature of the working fluid withinthe respective heat transfer device, or to measure the heat source fluidtemperature or heat sink fluid temperature.

The control system 135 can be a general system including sub-componentsthat perform distinct steps. For example, the control system 135includes the power supply 250 (such as, for example, a battery, arectifier, or other electric source) that supplies a direct currentelectric power to the compressor 105.

Moreover, the control system 135 can include one or more of digitalelectronic circuitry, computer hardware, firmware, and software. Thecontrol system 135 can also include appropriate input and outputdevices, a computer processor, and a computer program product tangiblyembodied in a machine-readable storage device for execution by aprogrammable processor. The procedure embodying these techniques(discussed below) may be performed by a programmable processor executinga program of instructions to perform desired functions by operating oninput data and generating appropriate output. Generally, a processorreceives instructions and data from a read-only memory and/or a randomaccess memory. Storage devices suitable for tangibly embodying computerprogram instructions and data include all forms of non-volatile memory,including, by way of example, semiconductor memory devices, such asEPROM, EEPROM, and flash memory devices; magnetic disks such as internalhard disks and removable disks; magneto-optical disks; and CD-ROM disks.Any of the foregoing may be supplemented by, or incorporated in,specially-designed ASICs (application-specific integrated circuits).

The controller 135 receives information from components (such as thetemperature sensors and the compressor 105) of the system 100 andcontrols operation of a procedure (as discussed below) that can eithermaintain the heat source or the heat sink at a relatively constanttemperature condition. Additionally, controlling the operation of anelectrochemical compressor 105 consists of turning its current on or offthrough the power supply. Alternatively, the voltage applied to theelectrochemical compressor 105 can be set to be in proportion to theheat source fluid temperature or the heat sink fluid temperature. Insome applications, such as electric cars without internal combustionengines, there may be an advantage in operating the vehicle airconditioning system electrically and driving each wheel independentlywithout a central motor (required to drive the air conditioning system).

The refrigeration system 100 can also include one-way valves 150, 155 atthe output of the compressor 105. The one-way valve 150, 155 can be anymechanical device, such as a check valve, that normally allows fluid(liquid or gas) to flow through it in only one direction (the directionof the arrows). The valves 150, 155 ensure proper delivery of thecomponents of the working fluid that exit the compressor 105 into therest of the refrigeration system 100 by reducing or avoidingback-pressure into the last cell in the compressor 105, and thereforeensure unidirectional flow of the fluids (which include gases). Forexample, the valve 150 is placed within a conduit 152 that transportsthe high pressure electrochemically active component plus the smallamount of water that is involved in the electrochemical process and thevalve 155 is placed within a conduit 157 that transports the condensablerefrigerant that bypasses the electrochemical process.

The refrigeration system 100 can also include a dryer 160 that isconfigured to remove water from the working fluid prior to reaching theexpansion valve 120 to reduce the chance of water freezing within thevalve 120 and potentially clogging the valve 120, and to increase theefficiency of the expansion process within the valve 120.

Referring also to FIG. 3A, in another implementation, theelectrochemical compressor 105 includes a plurality of cells 300, 301,302, 303 arranged in series with each other, with the first cell 300receiving the low pressure working fluid 200 from the conduit 112 anddiverting the low pressure refrigerant along conduit 305. In thisimplementation, only the first cell 300 diverts the low pressurerefrigerant along the conduit 305. An output 310 from the first cell 300is a higher pressure mixture of the electrochemically active componentand water; the output 310 is fed into an input 311 of the second cell301. Likewise, an output 312 from the second cell 301 is fed into aninput 313 of the third cell 302, and an output 314 of the third cell 302is fed into an input 315 of the fourth cell 303. An output 316 from thefourth cell 303 carries the high pressure mixture of theelectrochemically active component and water, and this output is mixedwith the diverted refrigerant in conduit 305, as discussed above, anddirected along conduit 116 toward the second heat transfer device 115.

As shown in FIG. 3A, the power supply is connected to the anode andcathode collector of each of the cells 300, 301, 302, 303. In otherimplementations, the anode collector of the cell 300 and the cathodecollector of the cell 303 are the only collectors connected to the powersupply. In this case, the end plates of each cell receive all thecurrent and the current is then “conveyed” across the cells.

Referring to FIG. 3B, in another implementation, the electrochemicalcompressor 105 includes a plurality of cells 320, 321, 322 arranged inseries with each other, with the first cell 320 receiving the lowpressure working fluid 200 from the conduit 112 and diverting the lowpressure refrigerant along conduit 325. In this implementation, the lowpressure refrigerant is mixed with the higher pressure mixture of theelectrochemically active component and water directed through an outputafter each of the cells 320, 321, 322 and each of the cells 320, 321,322 diverts the low pressure refrigerant. Thus, output 330 from thefirst cell 320 is a higher pressure mixture of the electrochemicallyactive component and water and this mixture is mixed with the divertedlow pressure refrigerant traveling in the conduit 325 to form a mixtureof the higher pressure electrochemically active component, the water,and the refrigerant that is directed to an input 331 of the second cell321. An output 333 from the second cell 321 is a higher pressure mixtureof the electrochemically active component and water and this mixture ismixed with the diverted low pressure refrigerant traveling in conduit332 to form a mixture of the higher pressure electrochemically activecomponent, the water, and the refrigerant that is directed to an input334 of the third cell 322. Lastly, an output 336 from the third cell 322is a higher pressure mixture of the electrochemically active componentand water and this mixture is mixed with the diverted low pressurerefrigerant traveling in conduit 335 to form a mixture of the higherpressure electrochemically active component, the water, and therefrigerant that is directed along conduit 116 toward the second heattransfer device 115.

As shown in FIG. 3B, the power supply is connected to the anodecollector of the first cell 320 and to the cathode collector of thethird cell 322. In this case, the end plates of each cell receive allthe current and the current is then “conveyed” across the cells. Inother implementations, the anode collector and cathode collector of eachof the cells 320, 321, 322 are connected to the power supply.

Referring to FIG. 3C, in another implementation, the electrochemicalcompressor 105 includes a plurality of cells 350, 351, 352, 353 arrangedin parallel with each other, with each of the cells 350, 351, 352, 353receiving the low pressure working fluid 200 from the conduit 112 andeach of the cells 350, 351, 352, 353 diverting the low pressurerefrigerant along respective conduits 360, 361, 362, 363. In thisimplementation, the low pressure refrigerant from each of the cells 350,351, 352, 353 is mixed together and passed through conduit 364, and thehigh pressure mixture of the electrochemically active component andwater directed through respective outputs 370, 371, 372, 373 of each ofthe cells 350, 351, 352, 353 is mixed together and passed throughconduit 374. These two mixtures in the conduits 364 and 374 are combinedwith each other and directed along the conduit 116 toward the secondheat transfer device 115.

The power supply can be connected to the anode collector and to thecathode connector of each of the cells 350, 351, 352, 353.

While three or four cells are shown in these drawings, it is noted thatany number of cells can be used in the compressor 105, and the number ofcells can be selected depending on the cooling application of the system100.

Referring also to FIG. 4A, the system 100 performs a procedure 400 fortransferring heat from the heat source at the first heat transfer device110 to the heat sink at the second heat transfer device 115.

Low pressure working fluid 200 (which is typically a gas mixture ofhydrogen, condensable refrigerant, and water) enters compressor 105(step 405). A mixture of hydrogen and water is dissociated from thecondensable refrigerant (step 410). In particular, the hydrogen (in theform of a proton) and water dissolve into the ion exchange media whilethe condensable refrigerant does not. The condensable refrigerant isdiverted along a path separate from the electrochemical path through themembrane electrode assembly (step 415). The dissociated mixture is thenpumped across the membrane electrode assembly of each cell in thecompressor 105 (step 420). In particular, electrons are stripped fromthe hydrogen in the hydrogen/water mixture at the anode collector of thecell, and the hydrogen ions are transported across the anode,electrolyte, and toward the cathode due to the electrical potentialapplied across the collectors from the power supply. Additionally, thehydrogen ion gas is pressurized across the membrane electrode assembly.Next, the hydrogen ions are recombined with the electrons at the cathodecollector to reform hydrogen gas at a higher pressure, and this higherpressure hydrogen gas is recombined with the diverted condensablerefrigerant to thereby raise the pressure of the working fluid (step430).

Thus, the electrochemical compressor 105 raises the pressure of theworking fluid 200 and delivers the higher pressure working fluid 200 tothe second heat transfer device (the condenser) 115 where thecondensable refrigerant is precipitated by heat exchange with the sinkfluid (step 435). The working fluid is then reduced in pressure in theexpansion valve 120 (step 440). Subsequently, the low pressure workingfluid is delivered to the first heat transfer device (the evaporator)110 where the condensed phase of the working fluid is boiled by heatexchange with the source fluid (step 445). The evaporator effluentworking fluid may be partially in the gas phase and partially in theliquid phase when it is returned from the evaporator to theelectrochemical compressor 105. In the process, heat energy istransported from the evaporator to the condenser and consequently, fromthe heat source at a relatively lower temperature to the heat sink atrelatively higher temperature.

Referring also to FIG. 4B, concurrently with the procedure 400, thecontrol system 135 performs a procedure 450 for controlling the amountof electrical potential applies to the current collectors of thecompressor 105, and therefore also controls the amount of heat energytransported from the evaporator to the condenser. The control system 135receives information from the one or more sensors (for example,temperature or pressure sensors) in the system 100 indicating physicalcharacteristics (such as temperature or pressure) at key locations ofthe system 100 (step 455). The control system 135 analyzes theinformation (step 460) and determines whether physical properties of thesystem 100 need to be adjusted based on the analyzed information (step465). For example, the control system 135 can determine that a currentapplied to the compressor 105 (and therefore the current applied to theelectrode collectors) needs to be adjusted. As another example, thecontrol system 135 can determine that a flow rate of one or more of theheat sink fluid and the heat source fluid that transport heat from andto the devices 115, 110 needs to be adjusted. If the control system 135determines that a physical property of the system 100 should beadjusted, then the control system 135 sends a signal to the componentthat is affected to adjust the particular property (step 470). Forexample, the control system 135 can send a signal to the power supply toadjust the amount of current applied to the current collectors in thecompressor 105. Otherwise, the control system 135 continues to receiveinformation from the one or more sensors (step 455).

In summary, the system 100 includes an electrochemical cell of thecompressor 105 that compresses an electrochemically active component ofthe working fluid, and remixes the compressed (at high pressure)electrochemically active component (the first component) with thecondensable refrigerant (the second component) to elevate the pressureof the mixed gas working fluid in a vapor compression refrigerationcycle. In this way, the electrochemical compressor 105 is capable ofproducing high pressure hydrogen gas from a mixed component workingfluid having an electrochemically active component such as, hydrogen andat least one condensable refrigerant. In this arrangement, hydrogen iscompressed to a much higher pressure than the final working fluidpressure (that is, the pressure of the remixed working fluid), andbecause of this, the hydrogen when mixed with the lower pressurecondensable refrigerant is at the required higher pressure. The exactpressure requirements for the hydrogen stream depends on the volume ofcondensable refrigerant being pressurized in relation to the volume ofhydrogen, the desired final pressure requirements of the remixed workingfluid, and the targeted energy efficiency. The check valves 150, 155 areemployed to make sure the gas flows are maintained in the intendeddirections and that no back flow is allowed towards the cells of thecompressor 105.

The energy efficiency of the system 100 depends on the available surfacearea of the anode 205 and the cathode 210, and the current density andoperating voltage applied to the cells from the power supply. Highercurrent densities result in greater the resistive losses for the system100.

The size reduction of the compressor 105 is feasible because of itscellular design, and because it is operating using an electrochemicalprocess. If an application requires significant size reductions, theelectrode (the anode and the cathode) surfaces can be reduced, theapplied current densities and voltages can be increased, and as a resulta smaller mass of cells can be employed in the compressor 105. Thiswould result in an almost order of magnitude reduction in size andweight for the system 100 compared to conventional mechanical systems.

Since cooling capacity is linked to applied current and voltage, oneadvantage of this system is that it can more easily modulate from lowcapacity (that is, low current density at a specific voltage) to a highcapacity. A system 100 designed to operate at high capacities actuallybecomes more efficient at lower utilizations, while, the opposite istrue for mechanical systems.

Referring also to FIGS. 5 and 6, exemplary hybrid refrigeration systems500, 600 define a closed loop that contains a working fluid and includethe same components (for example, the electrochemical compressor, theheat transfer devices, and the thermostatic expansion valve) of thesystem 100. These systems 500, 600 also include mechanical compressors580, 680 operating in conjunction with the electrochemical compressors505, 605 in a hybrid fashion. Such a design is useful for use inelectric vehicles, for example. The design of the systems 500, 600provides high efficiency service at low refrigeration requirements andallows the mechanical segment of the system 500, 600 to take over atconstant and higher refrigeration demands. The mechanical segment of thesystem 500, 600 is the segment that bypasses the electrochemicalcompressor 505, 605.

As shown in FIG. 5, the mechanical compressor 580 is in parallel withthe electrochemical compressor 505. For simplicity, the one way valves(such as the valves 150, 155) and the separate conduits for the highpressure electrochemically active component and the condensablerefrigerant (such as the conduits 152, 157) that are found at the outputof the compressor 505 are omitted from this drawing. As shown in FIG. 6,the mechanical compressor 680 is in series with the electrochemicalcompressor 605.

The refrigeration system 100, 500, 600 can work with a wide range ofcondensable refrigerants. However the choice of refrigerant depends onthe exact application under consideration and other external regulatoryfactors. Care should be taken in the selection of the refrigerant toensure that the refrigerant does not degrade the electrochemicalperformance of the system 100, 500, 600 or poison the electrocatalystemployed.

An ideal refrigerant has good thermodynamic properties, is noncorrosive,stable, and safe. The desired thermodynamic properties are at a boilingpoint somewhat below the target temperature, a high heat ofvaporization, a moderate density in liquid form, a relatively highdensity in gaseous form, and a high critical temperature. Since boilingpoint and gas density are affected by pressure, refrigerants may be mademore suitable for a particular application by choice of operatingpressure.

While we have described an electrochemical compressor that uses amultiple component working fluid utilizing hydrogen and that is based ona cationic exchange membrane, it is also possible to use a working fluidincluding chlorine as a component; such a working fluid could be usedadvantageously in an anionic exchange membrane cell. In anelectrochemical compressor using an anionic exchange membrane, theelectrochemically active component of the working fluid is first reducedat a cathode. The anions formed at the cathode migrate to the anodewhere they are oxidized. The gas evolved at the anode is at a higherpressure than the fluid entering the cathode. The process is the reverseof the cationic electrochemical compressor previously described abovewith reference to FIGS. 1-4B.

Other implementations are within the scope of the following claims.

What is claimed:
 1. A refrigeration system that conveys heat from afirst heat reservoir at a relatively low temperature to a second heatreservoir at relatively high temperature, the refrigeration systemdefining a closed loop that contains a working fluid, at least part ofthe working fluid being circulated through the closed loop, therefrigeration system comprising: a first heat transfer device thattransfers heat from the first heat reservoir to the working fluid, asecond heat transfer device that transfers heat from the working fluidto the second heat reservoir, an expansion valve between the first andsecond heat transfer devices that reduces pressure of the working fluid,a conduit system and an electrochemical compressor between the first andsecond heat transfer devices; wherein the electrochemical compressorcomprises: one or more electrochemical cells electrically connected toeach other through a power supply, each electrochemical cell comprising:a gas pervious anode, a gas pervious cathode, an electrolyte disposedbetween and in intimate electrical contact with the cathode and theanode; an electrochemical compressor input, an electrochemicalcompressor output, wherein at least one of said one or moreelectrochemical cells comprises an electrochemical compressor bypass;wherein the working fluid comprises: a condensable refrigerant thatessentially bypasses the electrochemical process and remains in theclosed loop ; and an electrochemically active fluid that participates inthe electrochemical process within the electrochemical compressor;wherein said conduit system receives at least oneelectrochemically-active fluid of said working fluid from saidelectrochemical compressor output and, other components of the workingfluid from said electrochemical compressor bypass, wherein said conduitsystem has a geometry that enables at least a portion of the receivedworking fluid to be imparted with a gain in kinetic energy as it movesthrough the conduit system.
 2. The refrigeration system of claim 1,wherein the electrolyte comprises a solid electrolyte.
 3. Therefrigeration system of claim 1, further comprising a temperature sensorthermally coupled to one or more of the working fluid, the first heattransfer device, and the second heat transfer device.
 4. Therefrigeration system of claim 1, wherein the condensable refrigerantdoes not participate in the electrochemical process.
 5. Therefrigeration system of claim 1, wherein the electrochemical compressorincludes: a cathode gas space on a nonelectrolyte side of the cathode:and an anode gas space on a nonelectrolyte side of the anode.
 6. Therefrigeration system of claim 1, wherein the electrochemical compressorincludes: a first electrochemically active route that traverses theanode and cathode: a second non-electrochemical route that bypasses theanode and cathode: and a combiner that combines the components that havetraversed the first and second routes.
 7. The refrigeration system ofclaim 1, wherein the first heat transfer device comprises a condenser.8. The refrigeration system of claim 1, wherein the second heat transferdevice comprises an evaporator.
 9. The refrigeration system of claim 1,further comprising a mechanical compressor in series with theelectrochemical compressor.
 10. The refrigeration system of claim 9,wherein the mechanical compressor is between the electrochemicalcompressor and the first heat transfer device.
 11. The refrigerationsystem of claim 9, wherein the mechanical compressor is between theelectrochemical compressor and second heat transfer device.
 12. Therefrigeration system of claim 1, wherein the working fluid includescarbon dioxide.
 13. The refrigeration system of claim 1, wherein theworking fluid includes a fluorocarbon gas.
 14. The refrigeration systemof claim 1, wherein the condensable refrigerant is not water.
 15. Therefrigeration system of claim 1, wherein the condensable refrigerantconsists essentially of water.
 16. The refrigeration system of claim 1,wherein the working fluid comprises water.